1520D - Same Differences.cpp

/** ========================================**
 ** @Author: Kareem Taha Abdelfatah
 ** @Category: Codeforces problems solutions
/** ========================================**/

#include<bits/stdc++.h>
#include<iterator>
using namespace std;
#define IO                  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
#define endll               "\n"
#define ll                  long long
#define fr(i, n)            for(ll i = 0; i < n; i++)
#define fr1(i, n)           for(ll i = 1; i <= n; i++)
#define asort(a)            sort(a + 1, a + n + 1)
#define dsort(a)            sort(a + 1, a + n + 1, greater<int>())
const long long N = 2e5 + 5, MOD = 1e9 + 7, oo = 1e18;
const double PI = 3.14;
const double Prox = 1e-7;
map<ll, ll>mp;
ll a[N];

int main()
{
    IO
    int tc; cin >> tc;
    while(tc--){
        mp.clear();
        ll n, ans = 0; cin >> n;
        fr1(i, n){
            cin >> a[i];
            mp[a[i] - i]++;
            ans += mp[a[i] - i];
        }
        cout << abs(n - ans) << endll;
    }
    return 0;
}